Low-income youth are overrepresented in the statistics on early onset oppositional defiant disorder (ODD) and conduct disorder (CD);however, low-income parents are least likely to engage in or be retained in the evidence-based behavioral parent training programs, which have proven to disrupt the escalation of ODD and CD behaviors. Consistent with Program Announcement (PAR-06-248), "From Intervention Development to Services: Exploratory Research Grants," this R34 project aims to develop and pilot-test use of Smartphone technology to enhance the engagement and retention of low-income parents of children (3 to 8 years old) with ODD and early CD behaviors in one evidence-based parent training program, Helping the Noncompliant Child (HNC;McMahon &Forehand, 2003). The Smartphone-enhanced HNC treatment program will be developed, and then tested in a pilot controlled trial in order to examine feasibility, cost-effectiveness, and consumer satisfaction, as well as trends in engagement and retention of parents and changes in parent and child behavior. Given that the early onset of ODD and CD behavior is the single most important predictor of delinquency, substance abuse, and violence for boys and girls in adolescence, the development of novel approaches to engage and retain low-income parents in evidence-based parent training programs is of critical public health importance.